Definition

Basically:

• Fail Safe = power off, it's unlocked
• Fail Secure = power off, it's locked

Electric locking devices include:

• Electric strikes
• Electromagnetic locks
• Electromechanical locks
• Electrified exit devices

Most electric strikes are sold fail secure by default. For example, if you order a Von Duprin 6123 24V US32D, and architectural grade 1 electric strike, it will most likely come fail secure regardless if it has Von Duprin's "FSE" (standing for fail secure) in the part number or not. The part number in the Von Duprin price book does not include "FSE." To be sure you are going to get a fail safe electric strike (not the norm) if that is indeed what you want, in this instance you would include Von Duprin's abbreviation for fail safe, "FS", for example, 6123 24V FS US32D.

All electromagnetic locks are fail safe because they are always unlocked when disconnected from the power source. Using a battery back-up does not make an electromagnetic lock fail secure because the magnet would still be unlocked if the power was disconnected. Later in this article it should become apparent why this detail is important for reasons of life safety.

Electromechanical locks include standard cylindrical or mortise locks that have been electrified and locks that are designed to only work electrically, such as an electric bolt lock. They are sold in equal amounts fail safe and fail secure.

Electrified exit devices come in a variety of functions, including those with electric latch retraction and those with electrified outside trim control. Electric latch retraction devices are fail secure whereas exit devices with electrified exterior trim control might be either fail safe or fail secure.

Application

Electric Strikes

Fail safe electric locking devices are used wherever doors must remain unlocked in the event of a fire or other life safety emergency. If the opening is fire rated, it must be positively latched by a fire rated device in the event of a fire. Therefore there is no such thing as a fire rated fail safe electric strike because if the power were off (as it might very well be during a fire) the door would not be positively latched. If you install a fail safe electric strike on a fire rated opening, the inspector can require you to replace the entire doorframe.

Technically, fire rated door frames cannot be modified in the field, but must be prepared for hardware (including architectural grade electrified hardware) in a fire rated shop. I have never heard of this being enforced, nevertheless, the AHD (Authority Having Jurisdiction) could enforce it, so if you plan to modify a fire rated opening in any way it might be a good idea to get the local fire marshal on board during the planning stages.

In general, a fail safe electric strike is a good choice for a "non-fire-rated door that must be unlocked in the event of an emergency other than a fire" kind of application.

Fail secure electric strikes are a good choice for exterior or other non-fire-rated doors where remote release or electronic access control is needed. They are pretty reliable, usually not difficult to install, and relatively inexpensive. One of the chief disadvantages of an electric strike is that, on out-swinging doors, they provide an opening into which a burglar can insert a tool, such as a tire iron, to pry directly on the locking device. A latch guard is a minimally effective deterrent to this kind of attack.

(Exterior doors are almost never fire rated, and if they are, usually it is because all the doors on the job were ordered to the same spec, not because they have to be.)

For more information about electric strikes, please visit:

http://hubpages.com/hub/Choosing-an-Electric-Strike

Electromagnetic Locks

Some inspectors and fire marshals just don't like electromagnetic locks. This is another reason to get your local AHD on board from the start. But if your AHD is not an obstacle, a mag can be a good solution for existing fire rated doors with existing fire rated hardware on them. The fire rated hardware can stay to keep the door positively latched in the event of a fire, and the mag is inherently fail safe, so it could be a good choice for stairwell doors, greatly simplifying the application. The problem with mag locks is that they lock both sides of the door simultaneously. That means you have to deal with both a means to get in (access control) and a means to get out (presence detector and redundant exit pushbutton, for example).

If the door already has an exit device, it is probably possible to install a request-to-exit (RX) switch in the bar to allow exit by a fully mechanical means - a factor which might make the AHD happier with the installation. The AHD will also want to know that all electromagnetic locks are wired so that the fire alarm will cut power to them in the event of a fire.

Since a mag lock does not positively latch, it cannot be legally used alone on a fire rated door. There must be a fire rated positively latching mechanism in addition to the mag.

Delayed egress electromagnetic locks can also be used for access control on egress doors while helping to prevent unauthorized exit. For more information on delayed egress, please visit:

http://hubpages.com/hub/delayed_egress

Electromagnetic locks are not too expensive and are very easy to install. Because they are inherently fail safe, you may want to install a battery back-up system so that they remain locked during routine power outages.

Electromechanical Locks

Fail safe electrified standard locks are ideal for stairwell doors (unless they already have exit devices) because they remain positively latched when unlocked. Many states and localities require that stairwell doors be unlocked in the event of a fire, and because all interior stairwell doors are fire rated, they must also remain positively latched.

In order to replace a standard mechanical lock with an electrified one, a raceway must be drilled through the door from lock side to hinge side so that wire can be run to power the lock. If you guessed that, technically speaking, this voids the fire rating on a fire rated door, you were correct. Be sure to clear all modifications to fire rated openings in advance with the local AHD.

Electric bolts are usually used as a last resort when no other application will work, such as when retrofitting access control to automatic sliding doors. Electric bolts are most commonly used in prisons, where egress concerns are treated rather differently than commercial applications. They can also be used in place of electromagnetic locks, however electric bolts designed for commercial (rather than detention) applications are less secure, less durable and more difficult to install than mag locks.

Electrified Exit Devices

If a door has an existing exit device or an architect has specified an exit device for an opening, it is because the capacity of the building in terms of the number of people therein warrants the use of an exit device. Therefore it is unwise to replace an exit device with another kind of hardware.

Luckily, many exit devices can be electrified in the field either by replacing internal parts of the device or by adding an electrified trim (outside handle or lever).

As I mentioned earlier, exit devices can be electrified in one of two ways:

• Electric latch retraction
• Electrified outside trim

Since electric latch retraction is always fail secure, it might not be a good choice for stairwell doors unless it was always unlocked from the stairwell side. If that were the case, the only probable purpose for the electric latch retraction would be to unlatch the door for a power operator (automatic door opener).

Electric latch retraction is ideal on exterior pairs of doors where fail secure access control is required. Since exterior pairs of doors are often equipped with concealed vertical rod exit devices, installing electric latch retraction is often the easiest and best alternative. Electric latch retraction (or electric remote dogging) is also very compatible for use with power operators.

The down side of electric latch retraction, in addition to being expensive in its own right, is that it often requires a special and expensive power supply. Sargent 56 prefix exit devices are an exception, requiring only a minimal power supply for activation.

Fail safe electrified exit device trim is a good alternative for stairwell doors whether they already have an exit device or not. For one thing, since the wire powering the trim is run through the exit device, no modification of the fire rated door is necessary.

Electrified exit device trim is also available fail secure, and is often a less expensive alternative to electric latch retraction where simple access control is the goal.

Note on "Continuous Duty"

I have been asked, ‘What is the difference between fail safe and continuous duty?' Fail safe applies to the function of the device as described above whereas continuous duty simply means the strike is built to be constantly powered if so required. The confusion arises, I think, because all fail safe locking devices are continuous duty. This is because a fail safe device must have power to be locked. Fail secure electric strikes that are connected to a timer and powered all day to remain unlocked also must be continuous duty rated. Therefore, not all continuous duty electric strikes are fail safe, but all fail safe strikes are continuous duty.

Rule of thumb: almost every kind of electric locking device that runs on DC current is continuous duty.